1. Field of the Invention
This invention relates to a method of producing an iron-, nickel-, or cobalt-base alloy of high purity, and more particularly to a method of producing an alloy containing at least one major ingredient selected from the group consisting of iron (Fe), nickel (Ni), and cobalt (Co) and having low contents of oxygen, sulphur, and nitrogen.
2. Description of the Prior Art
The inventors disclosed a method of producing nickel-base alloys with low contents of oxygen and sulphur in their Japanese Pat. No. 992,541, a method of deoxidizing and desulphurizing molten steel in Japanese Patent Publication No. 849/79, and a method of producing clean steel with low contents of oxygen, sulphur, and nitrogen in their Japanese Patent Laid-open Publication No. 58,010/77.
The essence of the above-mentioned methods of the inventors is in that an iron alloy is melted in a container which is lined with a basic refractory mainly consisting of calcium oxide (CaO); and aluminum (Al) or an aluminum alloy is added into the molten iron alloy in vacuo or in an argon atmosphere, accompanied with violent agitation if necessary, so as to remove oxygen and sulphur from the molten iron alloy by aluminum (Al), while the calcium oxide (CaO) in the basic refractory of the container lining is reduced by aluminum (Al) to isolate calcium (Ca), which calcium (Ca) reacts with oxygen (O.sub.2) and sulphur (S) in the molten iron alloy to form calcium oxide (CaO) and calcium sulfide (CaS), whereby the iron alloy is deoxidized and desulphurized.
In general, calcium (Ca) has a high vapor pressure and evaporates at a temperature above 1,480.degree. C. Although it is known to deoxidize a molten metal by adding aluminum (Al) or titanium (Ti) or cesium (Ce) therein and then to desulphurize, deoxidize, and denitrify the molten metal by adding calcium (Ca) or a calcium alloy therein, such known use of calcium (Ca) has shortcomings in that the yield of calcium (Ca) is low due to the above-mentioned properties thereof and that the desulphurization, deoxidation, and denitrification are not very effective. On the other hand, the above-mentioned methods disclosed by the inventors produce calcium (Ca) by reduction along the entire contact surface between the molten metal and the refractory lining, so that effective desulphurization, deoxidation, and denitrification are effected as the reduced calcium (Ca) evaporates and disperses through the molten metal. The methods previously disclosed by the inventors are further characterized in that the contact area between calcium (Ca) and the molten metal is larger than that in the prior art, and a part of the calcium (Ca) is alloyed with metallic elements in the molten metal, so that the content thereof can be decreased to 0.001 to 0.03%. Such low content thereof indicates that the desulphurization, deoxidation, and denitrification are effectively carried out, as a salient feature of the methods.
However, the previously disclosed methods of the inventors have shortcomings in that, when the methods are carried out repeatedly by using the same container lined with a basic refractory mainly consisting of calcium oxide (CaO) as described above, the contents of oxygen and sulphur in the produced alloy increase with the number of repetition of using the methods. More particularly, the methods previously disclosed by the inventors are accompanied by a phenomenon that if the methods of producing the alloy are repeatedly carried out by using the same container, the rate of deoxidation and the rate of desulphurization are deteriorated.